This invention relates to a multi-band radio receiver and, in more particular, to an electronic tuning device for the multi-band receiver, in which the bands and the channels can be preset digitally.
The radio receiver has been improved in various manners according to the recent developments of electronic engineerings and one of the results is disclosed in Japanese Utility Model application No. 11353/1975 in which a preset type multi-band receiver has a varactor diode tuner and a control therefor. The control comprises a channel selector switch means, a memory to be addressed by outputs of the channel selector switch, an up-down counter to be set by a manual pulse generator signal or a channel signal readout from the preset memory address and a digital-analog converter for converting an output of the counter into an analog signal, which is to be supplied to the variable capacitor (Varactor) diode equipped in a radio receiver which forms a tuning circuit reponsive to the analog signal for tuning it to a desired signal in the preset channel.
In this case, the channel selector switch means is composed of plurality of non-lock type switches.
The up-down counter is controlled by the output of the memory every time a channel selector signal from either one of the channel selector switches is detected. For a multi-band receiver, a band selector switch may be converted to the channel selector switches in series therewith.
In this case, however, since the output of the channel selector switch is different from that of the band selector switch in the standby state, that is, all of contacts of the channel selector switches are in off-state or low state, while band selector switch is on except instances of the band selection between the adjacent bands. Therefore, in order to detect the outputs of the both switches having different standby states, at least two kinds of circuits are necessary.
Further, although this type electronic tuner allows a relatively large number of preset informations to be set reliably, the channel selection becomes relatively complicated because the memory supplies the information to the up-down counter according to the output of the channel selector switch. In other words, assuming, for example, that the channel is to be changed from channel number 3 in A band to channel number 3 in B band, that is, when the channel is changed from a certain channel number in one band to the same channel number in an other band, it is necessary to operate, the channel selector switch contact corresponding to channel 3 again after the band selector switch is switched from A to B.
In addition to these defects, a chattering noise problem is severe because it utilizes a mechanical switch contact mechanism. That is, in this electronic tuning system, the outputs of mechanical switches are very important and if the outputs include chattering noises the system may malfunction. In order to eliminate the chattering problem, it has been usual to make the construction of the switch system itself special or to provide various chattering noise cancelling circuits.
However, these solutions make the system complex, expensive and unreliable.